This invention relates to radial ply pneumatic tires for vehicles and more particularly to such tires having inserts between the tread and carcass thereof.
The shoulders or lateral areas of tire treads presently known in the art tend to wear at a greater rate than the central portion of the tread. This necessitates the premature scrapping of such tires due to their total wear in the shoulder area although the central portion of the tread is still satisfactory for substantial additional service. The non-uniform distribution of tread wear is due in substantial measure to the severe conditions of service under which the tire mist operate. It is especially due to frequent sharp turns which cause complete wear in the shoulder area before comparable wear occurs in the central portion of the tread.
In an attempt to overcome the drawbacks in presently known tires it has been suggested, for example, that additional rubber be incorporated in the lateral area of the treads so that, notwithstanding the fact that this area of the tread wears more quickly than the central area thereof, both the central and lateral portions of the tread will wear out at approximately the same time. This solution however has undesirable side effects. For example, it causes an unwanted weight increase in the shoulder region which increases the heat build-up in the tire, thereby deleteriously affecting tire life. Further, increasing the quantity of material in the shoulder regions serves to increase the cost of manufacture of the tire. Another solution to the instant problem is disclosed in U.S. Pat. application Ser. No. 359,935 filed May 14, 1973, now U.S. Pat. No. 3,853,164 and assigned to the assignee of the instant invention. This application teaches the use of a cushion constituted by a material which is harder than the material from which the tread is constituted disposed between the tread and the breaker of the tire. The cushion extending to one or both of the lateral or outside walls of the tire. This solution also is not completely satisfactory because the use of such a hard cushion and has resulted in a ride quality which is substantially rougher than that of conventional tires. Further, it has been found that the use of such a hard cushion tends to reduce the traction of the tire, and is therefore potentially hazardous.